I was referred to Amazon by a friend for an internship position. Amazon, given their high number of applicants, does a good number of phone interviews. I ended up making it past the first round and to the third phone interview.
The first interview I believe was meant to be the most difficult, but my interviewer was very nice and we ended up going over the interview time chatting about various tech stuff.
The second and third interviewers came off as either nervous or uninterested (the former more so for the second, the latter for the third). I didn't manage to get the same rapport that I had developed with my first interviewer, but the second interview went alright.
The third interview comprised the second round. While I had liked my first two interviewers, this one seemed aloof and uninterested in doing the interview. This was the overdesign interview.
Amazon was one of few companies who actually got back to me and said that they were "pursuing other candidates", which was nice if disappointing. The best advice I can give is to be relaxed and understand that you know what you know. Your interviewers are just people and are probably as nervous as you about giving a good interview. Don't overcomplicate things, whatever you do.